The present invention relates generally to downhole tools for use in oilfield drilling operations. More particularly, the present invention relates to the transmission of power and/or data between downhole tools in a drill string and a downhole control sub (or, alternatively, the surface) through coupled inductors located on the longitudinal ends or shoulders of rotating tubular members, such as on the ends or shoulders of a mud motor.
As is well known in the industry, hydrocarbons are recovered from underground reservoirs, by drilling borehole or wellbore with a rotating drill bit attached to the bottom of a drilling assembly. The drilling assembly is attached to the bottom of a tubing member, which can be either rigid or flexible. The apparatus comprising the tubing is commonly referred to as the “drill string” consists of a long string of sections of drill pipe that are connected together end-to-end through threaded pipe connections. When a jointed pipe is employed as the drill string, the drill bit is either rotated by rotating the drill string from the surface and/or by a mud motor located proximate the drill bit at the distal end of the drill string. During drilling, a drilling fluid known as “drilling mud” or “mud” is supplied under pressure into the drill string to provide lubrication and cool the drill bit, as well to carry debris created by the drill bit during the drilling of the wellbore, such as for example, drill cuttings. The fluid exits through ports located in the drill bit at the end of the drilling assembly.
A mud motor drive shaft located within the drill string can be rotated by the passage of the drilling fluid at high pressure through the drill string assembly. Typically, drilling fluid is pumped from the surface to the drill bit through the bore of the drillstring, and is allowed to return with the cuttings through the annulus formed between the drillstring and the drilled borehole wall. Various conventional arrangements for drilling can employ a first tubular member which is rotationally moved by the rotation of the rotary table at the surface and which provides a connection to a second tubular member which moves independently of said first tubular member. The benefits of sensing and actuating movement of the drill bit independently of the rotation of the rotary table warrants placement of sensors at or near the drill bit to provide signals relating to speed and direction. Conveying signals from these sensors can pose problems if the drill bit assembly moves at speeds varying from the movement of the upper tubular members. Additionally, in conventional drilling applications, some types of bits assemblies have been developed to employ shock absorber systems allowing recoil from the drill bit to be isolated from the drill string. If a drill bit provides sensors which detect abnormal torque, bit hopping or bit bounce, the movement of the rotary table can be selectively altered to minimize shocks to the drill string. Modern sensors can use this data to modify rotary speed and direction signals to the drill bit assembly. The present invention can be utilized to provide communication path from the drill bit to the control sub or the surface.
Directional drilling is the intentional deviation of the wellbore from the path it would naturally take. In directional drilling, the drill string can include a rotary steerable system (RSS) which forces the drillstring to move in a desired path. Other types of deviation means include a bent sub which remains in fixed relation to the desired target zone. While a bent sub cannot be rotated from the surface, since it must remain in fixed orientation to the target zone, a rotary steerable system can be activated to directionally drill a bore while continuously being rotated by a standard rotary drilling rig. Continuous drill string movement is desirable because it is thought to aid in the prevention of sticking the drillstring in the borehole, thereby avoiding expensive pipe recovery operation.
Mud motors have become widely used in directional drilling assemblies. Generally, these motors provide a fixed member or stator and a rotating member or rotor, wherein the rotor is powered by the high pressure flow of drilling fluid through the drillstring thereby providing motive force to the drill bit assembly connected to the rotor.
Communication during drilling operations between the downhole tools and components generally located below the mud motor and other downhole control subs containing processing equipment located above the mud motor, or even the surface, is critical for real time monitoring and control of variables associated with the tools.
Heretofore, acoustic signaling systems were limited to 8 bits per second transmission rates which are hardly satisfactory to obtain real-time information concerning the status or location of the drill bit assembly. Alternate methods of communicating with downhole drill string tools include the use of wireline control. Wireline control, which allows for the transmission of up to 1200 bits per second, requires a separate conductor. The separate conductor can obstruct the wellbore and can be damaged during the insertion and removal of tools from the wellbore.
Another method of communicating information is a wired assembly wherein a conductor runs the length of the drill string and connects the components of a drill string to the surface, as well as to each other. In U.S. Pat. No. 6,655,460, Bailey et al. disclose a method for transmitting a signal and/or power between the surface and any component in the drill string through the use of a wired pipe. The advantage obtained is a higher capacity for transmitting information in a shorter amount of time. However, these systems can have problems in transferring signals between sequential joints in a drill string.
U.S. Pat. No. 6,392,317 to Hall et al. discloses an annular wire harness for use inside a section of drill pipe for communication of power and data through the drill pipe.
U.S. Pat. No. 6,515,592 to Babour et al. discloses an apparatus and method for providing electrical connections to permanent downhole oilfield installations using an electrically insulated conducting casing.
U.S. Pat. No. 6,427,783 to Krueger et al. and U.S. Pat. No. 6,540,032 to Krueger disclose a method for the contact-less transfer of power across a non-conductive radial gap of rotating and non-rotating members of a steering module.
In U.S. Pat. No. 6,641,434, expressly incorporated herein by reference, Boyle et al. disclose a method for the use of inductive couplers in a wired pipe joint for communication with the drillstring.
None of the existing communication transmission systems allow or permit communication through an interface between two independently moving tubular members in a well bore. While the present invention is not limited to a mud motor application, a preferred embodiment shown herein provides the most efficient means of discussing the structure and benefits of the present invention. Use of the mud motor embodiment should not be construed to limit this invention to mud motor connections.